Process for processing inorganic matter containing residue

ABSTRACT

A process and system provide for processing inorganic matter-containing residue in a thermal decomposition process. The process and system are effective for reducing pressures which can occur during processing of inorganic matter-containing residue. A process for processing inorganic matter-containing residue in a thermal decomposition process includes conveying inorganic matter containing residue from a thermal decomposition unit to a burn-out section and conveying the inorganic matter containing residue from the burn-out section through a transition section to an ash sump. The inorganic matter containing residue is cooled to remove about 10% or more of heat in the inorganic matter containing residue before reaching the ash sump. The process further includes contacting the inorganic matter containing residue with a cooling medium in the gas sump and venting gaseous material generated back to the thermal decomposition unit.

This application claims the benefit of U.S. Provisional Application No. 61/902,520, filed Nov. 11, 2013 and U.S. Provisional Application No. 61/907,232, filed Nov. 21, 2013, which are incorporated in their entirety herein by reference.

A process provides for processing inorganic matter containing residue during thermal decomposition of a carbonaceous material feedstock. More specifically, the process is effective for cooling inorganic matter containing residue and preventing pressure build-up.

BACKGROUND

Thermal decomposition processes, often referred to as gasification, include processes that are effective to convert carbonaceous feedstock, such as municipal solid waste (MSW) or coal, into a combustible gas. The gas can be used to generate electricity, steam or as a basic raw material to produce chemicals and liquid fuels.

The thermal decomposition process includes feeding carbonaceous feedstock into a heated chamber (the thermal decomposition unit or gasifier) along with a controlled and/or limited amount of oxygen and optionally steam. In contrast to incineration or combustion, which operate with excess oxygen to produce CO₂, H₂O, SO_(x), and NO_(x), thermal decomposition processes produce a raw gas composition that includes CO and H₂. More specifically, the thermal decomposition process involves a partial oxidation or starved-air oxidation of carbonaceous material in which a sub-stoichiometric amount of oxygen is supplied to the gasification process to promote production of carbon monoxide as described in WO 2009/154788. Success of a gasification process greatly depends on quality of syngas produced. Increased content of carbon monoxide (CO) and hydrogen (H₂) is desirable in syngas produced.

As feedstock is heated in a thermal decomposition process, carbonaceous materials in the feedstock are converted into CO, CO₂ and H₂. Mineral matter in the feedstock along with any unconverted carbonaceous material or unconverted carbon form ash. The amount and composition of ash (e.g. carbon content) can have an impact on the smooth running of the decomposition process as well as on the disposal of ash. Processing of hot ash may result in steam generation and increased pressure in processing equipment.

SUMMARY

A process and system are provided for processing inorganic matter-containing residue in a thermal decomposition process. The process and system are effective for reducing pressures which can occur during processing of inorganic matter-containing residue. The process is effective for use during start-up where inorganic matter containing residue may have higher levels of carbon, as well as being effective after start-up.

A process for processing inorganic matter-containing residue in a thermal decomposition process includes conveying inorganic matter containing residue from a thermal decomposition unit to a burn-out section and conveying the inorganic matter containing residue from the burn-out section through a transition section to an ash sump. The inorganic matter containing residue is cooled to remove about 10% or more of heat in the inorganic matter containing residue before reaching the ash sump. The process further includes contacting the inorganic matter containing residue with a cooling medium in the ash sump and venting gaseous material generated back to the thermal decomposition unit.

In another aspect, a process for reducing pressure in a thermal decomposition unit includes conveying inorganic matter containing residue from a thermal decomposition unit through a transition section into an ash sump. The process includes cooling inorganic matter containing residue being conveyed through the transition section by contacting the inorganic matter containing residue with a cooling medium and conveyed through the transition section at a rate effective for removing about 10% or more heat in the inorganic matter containing residue before reaching the ash sump. Gaseous material generated from the ash sump is vented to the thermal decomposition unit to maintain a pressure in the ash sump of about 15 inches of water pressure (gauge pressure) or less.

In another aspect, a system for reducing pressure in a thermal decomposition unit includes a burnout section configured to receive inorganic matter containing residue; an ash ram effective for moving inorganic matter containing residue from a burnout section through a transition section and into an ash sump; a cooling medium sprayer configured to apply cooling medium to inorganic matter containing residue in the transition section; and a vent line effective for venting a gaseous material back to the thermal decomposition unit.

BRIEF DESCRIPTION OF FIGURES

The above and other aspects, features and advantages of several aspects of the process will be more apparent from the following figures.

FIG. 1 is a schematic diagram of a thermal decomposition apparatus that includes a gasification zone and a burn-up zone.

FIG. 2 is a schematic diagram of an aspect of a thermal decomposition apparatus that includes a gasification zone and a burn-up zone wherein the gasification zone includes four sections or hearths.

FIG. 3 is a schematic diagram of an aspect of a thermal decomposition apparatus that includes a gasification zone, a burn-up zone and a tar reduction zone wherein the gasification zone includes five sections or hearths.

FIG. 4 illustrates material flow through a thermal decomposition unit.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various aspects of the present process and apparatus. Also, common but well-understood elements that are useful or necessary in commercially feasible aspects are often not depicted in order to facilitate a less obstructed view of these various aspects.

DETAILED DESCRIPTION

The following description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary embodiments. The scope of the invention should be determined with reference to the claims.

Definitions

Unless otherwise defined, the following terms as used throughout this specification for the present disclosure are defined as follows and can include either the singular or plural forms of definitions below defined:

The term “about” modifying any amount refers to the variation in that amount encountered in real world conditions, e.g., in the lab, pilot plant, or production facility. For example, an amount of an ingredient or measurement employed in a mixture or quantity when modified by “about” includes the variation and degree of care typically employed in measuring in an experimental condition in production plant or lab. For example, the amount of a component of a product when modified by “about” includes the variation between batches in a multiple experiments in the plant or lab and the variation inherent in the analytical method. Whether or not modified by “about,” the amounts include equivalents to those amounts. Any quantity stated herein and modified by “about” can also be employed in the present disclosure as the amount not modified by “about”.

“Carbonaceous material” as used herein refers to carbon rich material such as coal, and petrochemicals. However, in this specification, carbonaceous material includes any carbon material whether in solid, liquid, gas, or plasma state. Among the numerous items that can be considered carbonaceous material, the present disclosure contemplates: carbonaceous material, carbonaceous liquid product, carbonaceous industrial liquid recycle, carbonaceous municipal solid waste (MSW or msw), carbonaceous urban waste, carbonaceous agricultural material, carbonaceous forestry material, carbonaceous wood waste, carbonaceous construction material, carbonaceous vegetative material, carbonaceous industrial waste, carbonaceous fermentation waste, carbonaceous petrochemical co products, carbonaceous alcohol production co-products, carbonaceous coal, tires, plastics, waste plastic, coke oven tar, fibersoft, lignin, black liquor, polymers, waste polymers, polyethylene terephthalate (PETA), polystyrene (PS), sewage sludge, animal waste, crop residues, energy crops, forest processing residues, wood processing residues, livestock wastes, poultry wastes, food processing residues, fermentative process wastes, ethanol co-products, spent grain, spent microorganisms, or their combinations.

The term “fibersoft” or “Fibersoft” or “fibrosoft” or “fibrousoft” means a type of carbonaceous material that is produced as a result of softening and concentration of various substances; in an example carbonaceous material is produced via steam autoclaving of various substances. In another example, the fibersoft can include steam autoclaving of municipal, industrial, commercial, and medical waste resulting in a fibrous mushy material.

The term “municipal solid waste” or “MSW” or “msw” means waste that may include household, commercial, industrial and/or residual waste.

The term “syngas” or “synthesis gas” means synthesis gas which is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or hydrocarbons to produce hydrogen, the gasification of coal and in some types of waste-to-energy gasification facilities. The name comes from their use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas is combustible and is often used as a fuel source or as an intermediate for the production of other chemicals.

“Ton” or “ton” refers to U.S. short ton, i.e. about 907.2 kg (2000 lbs).

In addition to carbon and hydrogen, feedstocks will include a certain quantity of inorganic incombustible material, often referred to by the term “ash,” which is separated during the complete or partial combustion of the feedstock. At certain temperatures, the ash may fuse to form agglomerates or “slag”. The process by which slag is formed is referred to as “slagging”.

Thermal Decomposition Unit Design and Operation

Some examples of suitable thermal decomposition processes and apparatus are provided in U.S. Ser. Nos. 13/427,144, 13/427,193 and 13/427,247, all of which were filed on Apr. 6, 2011, and all of which are incorporated herein by reference.

Referring now to FIG. 1, the thermal decomposition apparatus 10 includes a gasification zone 103 and a burn-up zone 200. The gasification zone may include one inlet for adding gas (e.g., oxygen containing gas, steam, carbon dioxide), inlet 102; and the burn-up zone may include one inlet for adding gas, inlet 202. The gasification zone 103 receives carbonaceous material feedstock 101. A transfer ram 710 moves a material bed of the feedstock through the thermal decomposition apparatus. A transfer ram face 715 may receive gas (e.g., oxygen containing gas, steam, carbon dioxide) and allow the gas to exit at its face.

A stream of solid ash 205 may be removed from burn-up zone 200. An ash transfer ram 720 may move ash out of the thermal decomposition unit. An ash transfer ram face 725 may receive gas (e.g., oxygen containing gas, steam, carbon dioxide) and allow the gas to exit at its face. A stream of raw syngas 105 may be removed from the gasification zone 103.

Referring now to FIG. 2, the gasification-apparatus 11 includes a gasification zone 113 and a burn-up zone 230. As shown in this aspect, the gasification zone 113 includes four gasification hearths: Hearth-I 310, Hearth-II 320, Hearth-III 330, and Hearth-IV 340. In other aspects, the gasification zone may include from 1 to 10 hearths. One or more of the gasification hearths may include a transfer ram 710. A transfer ram face 715 may receive gas and allow the gas to exit at its face.

Each gasification hearth includes one inlet for adding gas: gas inlet 111 to Hearth-I, gas inlet 121 to Hearth-II, gas inlet 131 to Hearth-III, and gas inlet 141 to Hearth-IV. The burn-up zone includes one inlet for adding gas: gas inlet 202. A carbonaceous material feedstock 101 can be added into Hearth-I (entry hearth) of the gasification zone 113. A stream of solid ash 205 can be removed from the burn-up zone 230. An ash transfer ram 720 may be utilized to move ash out of the thermal decomposition unit. An ash transfer ram face 725 may receive gas and allow the gas to exit at its face. A stream of raw syngas 105 can be removed from the gasification zone 113.

Referring now to FIG. 3, the gasification-apparatus 13 includes a gasification zone 143, a burn-up zone 500, a connecting zone or throat 300 and a tar reduction zone 400. The gasification zone 143 includes five gasification hearths: Hearth-I 110, Hearth-II 120, Hearth-III 130, Hearth-IV 140, and Hearth-V 150. Each gasification hearth includes one inlet for adding gas: gas inlet 611 to Hearth-I, gas inlet 621 to Hearth-II, gas inlet 631 to Hearth-III, gas inlet 641 to Hearth-IV and gas inlet 651 to Hearth-V. The burn-up zone includes one inlet for adding gas: gas inlet 202. The connecting zone or throat 300 includes one inlet for adding gas: gas inlet 301.

A carbonaceous material feed 101 can be added into Hearth-I (entry hearth) of the gasification zone 143. One or more of the gasification hearths may include a transfer ram 710. A transfer ram face 715 may receive gas and allow the gas to exit at its face. A stream of solid ash 205 can be removed from the burn-up zone 500. An ash transfer ram 720 may be utilized to move ash out of the thermal decomposition unit. An ash transfer ram face 725 may receive gas and allow the gas to exit at its face. A stream of hot syngas 405 can be removed from the tar reduction zone 400.

Burn-Out Section: FIG. 4 illustrates more detailed aspects of a thermal decomposition unit. In this aspect, feedstock material 101 moves into a feed hearth 820 and then a main hearth of a gasification zone 103. A transfer ram 710 moves material through the gasification zone 103. A poker arm 800 may extend from the transfer ram 710 into the material. Material moves into a burnout section 920. Solid ash 205 is conveyed through a transition section 822 into an ash sump 860 by an ash transfer ram 720. As ash 205 is conveyed through the transition section 822, the ash may be contacted with a cooling medium provided from one or more cooling medium sprayers 927. In this aspect, the process includes providing cooling medium through the cooling medium sparger 927 at a rate of about 5 to about 15 gallon per minute, in another aspect, about 6 to about 14 gallons per minute, in another aspect, about 7 to about 13 gallons per minute, in another aspect, about 8 to about 12 gallons per minute, and in another aspect, about 9 to about 11 gallons per minute.

In another aspect, the amount of cooling medium sprayed onto ash is a function of the amount of ash generated. In this aspect, a ratio of ash generated (in pounds per hour) to cooling medium applied (in gallons per hour) is about 2:1 to about 10:1, in another aspect, about 3:1 to about 9:1, in another aspect, about 4:1 to about 8:1, and in another aspect, about 5:1 to about 7:1.

In one aspect, feedstock material 101 follows a material path 840 through the thermal decomposition unit. In another aspect, gas 900 may be supplied to the transfer ram 710. Oxygen and steam may be introduced at one or more points in the burnout section 920. A stream of raw syngas 105 may be removed from the gasification zone 103.

In one aspect, feedstock is moved through the burn-out section at a rate effective for providing a retention time of feedstock in the burn-up zone of about 0.5 hours to about 5 hours, in another aspect, about 1 to about 4 hours, and in another aspect, about 2 to about 3 hours. In addition to containing non-carbonaceous mineral matter, solid ash may include unconverted carbon or unconverted carbonaceous matter.

The burn-out section is effective for reducing an amount of carbon in inorganic matter containing residue. In one aspect, carbon content of said solid ash leaving the burn-out section is less than about 10 wt %. In one aspect, carbon content of solid ash is less than 5 wt %. In one aspect, ratio of carbon content of solid ash to carbon content of carbonaceous material feed is less than about 0.1. In one aspect, ratio of carbon content of solid ash to carbon content of carbonaceous material feed is less than about 0.01.

The carbon content of ash and carbon content of carbonaceous material feed refers to carbon or a chemical that contains carbon. In this aspect, numerous known techniques may be utilized to measure carbon content. Some examples of techniques that may be used to measure carbon include and are not limited to loss-on-ignition (LOI) tests, thermogravimetric analysis (TGA), laser probe based optical methods, methods using microwave radiation, methods using nuclear magnetic resonance (NMR), and various ASTM methods (see for example ASTM D6316).

Raw syngas is produced that may include carbon monoxide (CO) and carbon dioxide (CO₂). It is desirable to have more CO and less CO₂ in the raw syngas. In one aspect, the CO/CO₂ molar ratio in said raw syngas is greater than about 0.75. In one aspect, the CO/CO₂ molar ratio in said raw syngas is greater than about 1.0. In one aspect, CO/CO₂ molar ratio in said raw syngas is greater than about 1.5. Hot syngas may include carbon monoxide (CO) and carbon dioxide (CO₂). It is desirable to have more CO and less CO₂ in the hot syngas. In one aspect, the CO/CO₂ molar ratio in said hot syngas is greater than about 0.75. In one aspect, the CO/CO₂ molar ratio in said hot syngas is greater than about 1.0. In one aspect, CO/CO₂ molar ratio in said hot syngas is greater than about 1.5.

Transition Section and Ash Sump: As further shown in FIG. 4, ash 205 is conveyed through the transition section 822 into an ash sump 860. The ash sump 860 includes a cooling medium 922. In one aspect, the cooling medium 922 is water. Cooling medium 922 in the ash sump 860 is maintained at a cooling medium level 924. The cooling medium level 924 defines an open area 827 above the cooling medium 922. The cooling medium level 924 is effective for providing a water seal such that any gaseous material in open section 827 cannot vent into the environment through ash sump opening 832. Ash sump 860 includes a conveyor 947 which can continually remove wet ash for disposal in dumpster 948.

In one aspect, the ash ram is moved at a rate effective for allowing inorganic matter containing residue to cool to about 2700° F. or less as measured at the end of the transition section and prior to entering the ash sump. In another aspect, the inorganic matter containing residue cools to about 2600° F. or less, in another aspect, about 2500° F. or less, in another aspect, about 2400° F. or less, in another aspect, about 2300° F. or less, in another aspect, about 2200° F. or less, in another aspect, about 2100° F. or less, and in another aspect, about 2000° F. or less. In another aspect, the ash ram is moved for about 2 to about 5 seconds and then paused for about 8 to about 15 seconds, and in another aspect, the ash ram is moved for about 3 to about 4 seconds and then paused for about 9 to about 14 seconds. In one aspect, each ram push or ash ram frequency is about 1 push or less per hour, and in another aspect, about 1 push or less every two hours.

Vent Line: As ash 205 is conveyed through the transition section 822 and contacted with a cooling medium, the wet ash may form a gas tight seal in transition section 822. Vent line 930 is effective for dissipating any pressure that builds up in open area 827. Vent line 930 proceed through valve/control mechanism 940 and allow gaseous material to vent back into the thermal decomposition unit. In this aspect, the vent line is effective for maintaining a pressure in the ash sump of about 15 inches gauge or less of water pressure, in another aspect, the vent line is effective for maintaining a pressure in the ash sump of about 10 inches gauge or less of water pressure, and in another aspect, the vent line is effective for maintaining a pressure in the ash sump of about 5 inches gauge or less of water pressure. Venting back to the thermal decomposition unit is important as the gaseous material being vented back may include CO and ash.

In one aspect, application of cooling medium and movement of the ash ram is effective for providing about 500 to about 1000 pounds of steam per hour, in another aspect, about 600 to about 900 pounds of steam per hour, and in another aspect, about 700 to about 800 pounds of steam per hour. In another aspect, a ratio of an amount of steam (in pounds per hour) vented back to the thermal decomposition unit to a total amount of steam added to the thermal decomposition unit from other sources (in pounds per hour) is about 0.6 to about 1 or less, in another aspect, about 0.55 to about 1 or less, in another aspect, about 0.5 to about 1 or less, in another aspect, about 0.4 to about 1 or less, in another aspect, about 0.3 or less, in another aspect, about 0.25 or less, and in another aspect, about 0.1 to about 1 or less.

In another aspect, the amount of steam generated is a function of the amount of ash generated. In this aspect, a ratio of ash generated (in pounds per hour) to steam generated (in pounds per hour) is about 2:1 to about 6:1, and in another aspect, about 3:1 to about 4:1.

Feedstock: In accordance with the process, the feedstock material provided to the thermal decomposition units forms a moving material bed inside the thermal decomposition unit. A temperature of the material bed effects slagging. In this aspect, the process is effective for maintaining a material bed temperature not exceeding about 2300° F. at any point in the material bed, in another aspect, the material bed temperature does no exceed about 2200° F., in another aspect, about 2100° F., in another aspect, about 2000° F., in another aspect, about 1900° F., in another aspect, about 1800° F., in another aspect, about 1700° F., in another aspect, about 1600° F., in another aspect, about 1500° F., and in another aspect, the material bed temperature does not exceed about 1400° F. Temperature may be measured by any known methods, including for example the use of thermo-couples which are inserted into the material bed.

Feedstock/Oxygen: A carbonaceous material feed is introduced into the thermal decomposition unit. A first molecular oxygen containing gas is supplied to the gasification zone and thus the carbonaceous material feed is treated with molecular oxygen in order to initiate and facilitate chemical transformation of carbonaceous material. A portion of the carbonaceous material feed is gasified produce a first gaseous product. Supply of oxygen into the thermal decomposition unit is controlled in order to preferentially promote formation of carbon monoxide from carbonaceous material. A sub-stoichiometric amount of oxygen is supplied in order to promote production of carbon monoxide. In one aspect, oxygen is provided to the gasification zone at a rate of about 0.5 to about 1.5 lb-mol/hr-ft² of the thermal decomposition bed and in another aspect, about 0.75 to about 1.25 lb-mol/hr-ft² of thermal decomposition bed.

While the invention herein disclosed has been described by means of specific embodiments, examples and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims. 

What is claimed is:
 1. A process for processing inorganic matter-containing residue in a thermal decomposition process, the process comprising: conveying inorganic matter containing residue from a thermal decomposition unit to a burn-out section; conveying the inorganic matter containing residue from the burn-out section through a transition section to an ash sump, wherein organic matter containing residue is cooled to remove about 10% or more of heat in the inorganic matter containing residue before reaching the ash sump; contacting the inorganic matter containing residue with a cooling medium in the ash sump, wherein a gaseous material is generated; and venting the gaseous material back to the thermal decomposition unit.
 2. The process of claim 1 wherein the burn-out section is effective for reducing an amount of carbon in the inorganic matter containing residue.
 3. The process of claim 1 wherein inorganic matter containing residue is conveyed through the transition section with an ash ram.
 4. The process of claim 1 wherein the inorganic matter containing residue is cooled by spraying a cooling medium onto the inorganic matter containing residue in the transition section.
 5. The process of claim 4 wherein the cooling medium is water.
 6. The process of claim 3 where the ash ram is moved at a rate effective for allowing inorganic matter containing residue to cool to about 2700° F. or less.
 7. The process of claim 3 wherein the ash ram is moved for about 2 to about 5 seconds and then paused for about 8 to about 15 seconds.
 8. The process of claim 1 wherein the gaseous material includes steam.
 9. The process of claim 8 wherein a ratio of an amount of steam vented back to the thermal decomposition unit to steam added to the thermal decomposition unit from other sources is about 0.6 to 1 or less.
 10. The process of claim 8 wherein a ratio of ash generated to steam generated is about 2:1 to about 6:1.
 11. The process of claim 1 wherein a ratio of ash generated to cooling medium applied is about 2:1 to about 10:1.
 12. A process for reducing pressure in a thermal decomposition unit, the process comprising: conveying inorganic matter containing residue from a thermal decomposition unit through a transition section into an ash sump, wherein inorganic matter containing residue being conveyed through the transition section is contacted with a cooling medium and conveyed through the transition section at a rate effective for removing about 10% or more heat in the inorganic matter containing residue before reaching the ash sump; and venting a gaseous material from the ash sump to the thermal decomposition unit, wherein the process is effective for maintaining a pressure in the ash sump of about 15 inches gauge or less of water pressure.
 13. The process of claim 12 wherein inorganic matter containing residue is conveyed through the transition section with an ash ram.
 14. The process of claim 13 where the ash ram is moved at a rate effective for allowing inorganic matter containing residue to cool to about 2700° F. or less.
 15. The process of claim 13 wherein the ash ram is moved for about 2 to about 5 seconds and then paused for about 8 to about 15 seconds.
 16. The process of claim 12 wherein the cooling medium is water.
 17. The process of claim 12 wherein the ash sump includes a cooling medium.
 18. The process of claim 17 wherein the cooling medium is water.
 19. The process of claim 12 wherein the gaseous material includes steam.
 20. The process of claim 19 wherein a ratio of an amount of steam vented back to the thermal decomposition unit to steam added to the thermal decomposition unit from other sources is about 0.6 to 1 or less.
 21. The process of claim 19 wherein a ratio of ash generated to steam generated is about 2:1 to about 6:1.
 22. The process of claim 12 wherein a ratio of ash generated to cooling medium applied is about 2:1 to about 10:1.
 23. A system for reducing pressure in a thermal decomposition unit, the system comprising: a burnout section configured to receive inorganic matter containing residue; an ash ram effective moving inorganic matter containing residue from a burnout section through a transition section and into an ash sump; a cooling medium sprayer configured to apply cooling medium to inorganic matter containing residue in the transition section; and a vent line effective for venting a gaseous material back to the thermal decomposition unit.
 24. The system of claim 23 wherein the burnout section includes one or more addition points for addition of steam and oxygen in amounts effective for reducing an amount of carbon in the inorganic matter containing residue.
 25. The system of claim 23 wherein the ash ram is moved at a rate effective for allowing inorganic matter containing residue to cool to about 2700° F. or less.
 26. The system of claim 25 wherein the ash ram is moved for about 2 to about 5 seconds and then paused for about 8 to about 15 seconds.
 27. The system of claim 23 wherein the cooling medium is water.
 28. The process of claim 23 wherein the ash sump includes a cooling medium.
 29. The process of claim 28 wherein the cooling medium is water.
 30. The process of claim 23 wherein the gaseous material includes steam.
 31. The process of claim 30 wherein a ratio of an amount of steam vented back to the thermal decomposition unit to steam added to the thermal decomposition unit from other sources is about 0.6 to 1 or less.
 32. The process of claim 30 wherein a ratio of ash generated to steam generated is about 2:1 to about 6:1.
 33. The process of claim 23 wherein a ratio of ash generated to cooling medium applied is about 2:1 to about 10:1. 